Various display terminals and network environments have been developed in recent years. Because of this, the NT (Joint Video Team) has undertaken an examination of the SVC (Scalable Video Coding) encoding system which enables scalability of space/time/SNR (Signal to Noise Ratio) for AVC (Advanced Video Coding) (see, for example, Non-patent document 1).
In SVC, three prediction methods, namely, Inter prediction, Intra prediction, and Interlayer prediction are used, and redundancy elimination interposed between times, spaces, and layers is performed. Examples of prediction modes obtainable via SVC are given below.
[Inter Prediction]
                Skip mode (Skip)        Direct mode (Direct)        16×16 block size motion prediction mode (P16×16)        16×8 block size motion prediction mode (P16×8)        8×16 block size motion prediction mode (P8×16)        8×8 block size motion prediction mode (P8×8)[Intra Prediction]        16×16 block size Intra prediction mode (I16×16)        8×8 block size Intra prediction mode (I8×8)        4×4 block size Intra prediction mode (I4×4)[Interlayer Prediction]        BLSkip mode (BLSkip)        IntraBL mode (IntraBL)        
When P8×8 is being performed, each 8×8 block can be further divided into 8×4, 4×4, and 4×4 block sizes. In SVC, one of these candidates for prediction mode search (prediction mode search candidates) is selected as the optimum prediction mode in each macro block.
An example of a method used to decide the optimum prediction mode is given below.
In JSVM (Joint Scalable Video Model: see, for example, Non-patent document 2) which is promoted by JVT as an SVC reference encoder, the encoding costs which are generated by the coding bit and encoding distortion are calculated in each prediction mode, and the prediction mode having the lowest encoding costs out of all the aforementioned prediction modes is determined to be the optimum prediction mode.
Moreover, in Patent document 1 given below, vectors are created by extrapolating or interpolating reference frame motion vectors in encoding subject frames, and the coordinates of each pixel in the macro-blocks that have moved as a result of this are then determined, and the number of times pixels coincide are counted for each pixel. Next, the prediction mode search candidates are narrowed down in accordance with the size of the value of a score which is calculated from the count number of each pixel within the encoding target macro-blocks. The method used for this narrowing down is one that was proposed in order to increase the speed of an H.264/AVC prediction mode search, however, it can also be applied in SVC which is a mechanism for the same prediction mode search as in H.264/AVC.
Moreover, in Patent document 2 given below, in order to make it possible to perform the intra-frame encoding at high-speed, for example, nine intra-frame prediction errors are determined in a block where intra-frame encoding is to be performed using the pixel values of adjacent encoding blocks and, based on these prediction errors, a prediction mode is decided for that block. Next, a prediction mode for that block is decided using the intra-frame prediction mode of an adjacent block that have already been encoded, and when the two prediction modes match, the prediction mode is selected as it is. If, however, the two prediction modes do not match, the prediction mode having the lower encoding costs is selected.